Pulverizing machine



March 18, 1930.- w. K. LIGGETT 1,751,009

PULVERIZING MACHINE Original Filed May 20, 1918 2 Sheets-*Sheet l M. .Qd

W. K. LIGGETT PULVERIZING MACHINE original Filed May 20, 1918 2 Sheets-Sheet 2 A'rORNEY.

Alat'entefl Mar. 1s, V1930 *"UVNrrED STATES infants` WILLIAM xELsEY LICGTT, oF COLUMBUS, omo, AssICfNon rro "ran JEFFREY MANU- FACTURING COMPANY, or COLUMBUS, cmo, A CononarIoN orv omo PULVERIZINC MACHINE Application led May 20, 1918, Serial N'o. -235,635. v ReneWedJJuly 3Q, 1929.

.The present invention relates to certain adapted to engage and pulverize material and a hopper having feeding and confining chambers arranged to receive and feed the materi-l al to be pulverized and retain or confine it Within and return it to theinfluence or zone of action of the rapidly revolving -arms until 'it shall be reducedl to the desired degree of ineness. 'p

The especial object ofthis invention is'to provide an improved pulverizing machine which shall be adaptable to a wider range of 2o use. and which will operate with greater efficiency and uniformity 0f action than the machines heretofore manufactured.

The means whereby I attain this object are fully set forth in the following specification 525 and illustratedl in the accompanying drawings of which Fig. 1 is a sectional view of the preferred y embodiment of my invention taken along the line 1--1 of Fig. 2.

Fig. 2 is a sectional view taken along the line 2 2 'of F 1.

Fig. 3 is an elevation of the machine illustrated in Figs. 1 and 2. a

Figs. 4-and 5-4 are diagrammatic figures illustrating the action of the operative parts along the horizontal central Vplane of the.

"'roton The main frame 1 consists of end -f'walls 3 and side walls 4, formed of a single casting, provide-d along their lower edges with ianges 5 adapted to rest upon 'and be atof the machine upon the material being pultached to anysuitable foundation, and along their upper edges with flanges 6 to which the housing 2 may be bolted. Upon the end walls 3 are formed ,outwardly extending flanges, or

shelves, 7l to which are bolted the bearing housing 8. Within the 'bearing Vhousing 8 are mounted suitable ball bearings 9 on which the rotary element of the machine is supported.

PArENnoFrlcr.

The inner races 10 of these ball bearings are fitted to the shaft-'11 which extends longitudinally through the machine. Mounted up# on the shaft 11 between the bearings are a plurality of disks 12 which are held in spaced i relation by spacing collars 13 and are clamped in place between the end disks 14 which have outwardly extending hubs engaging the inner ends-of the ball .bearing Vraces 10. Screw threaded to the shaft 11 are clamping nuts 15 arranged to draw these parts togetherto form a drum likerotor upon which the active elements of the. machine are mounted. To the pro]ecting end of this shaft 11 is attached a pulley 16 adapted to be connected through a suitable belt with any convenient source of rotative power to cause tlieVrapid'l revolution of the rotor.

Extending longitudinally of the shaft 11 and supportedin apertures of the disks 12;and 14 are a plurality of pivot rods 17 upon each of which arepivotally mounted a plurality of arms 18 adapted, when the rotor rapidly revolves, to assume positions substantially radial to the center of such rotation. When this rotor is caused to revolve at high velocity the outer ends of the arms 1 8 will generate a substanv tially continuous cylindrical surface upon which the material to be pulverized will float' during the process of pulverization, and Which will be hereinafter referred to as the pulverizing surface. rIt will be noted from rotor V6 axially 'extending rows-of arms are provided. Itvwill be noted that the visible arms of three of the rows are-on one side `of a plate 12 while the Avisible arms of the other threerows are on the other sideof the same plate. It will be further evident from Figure 1 that the arms of each row are disposed between alternate pairs of platesand it'follows from- Fig. 2 that arms of the succeeding 'row arey disposed in the intervening spaces. Consequently, starting for example with thel face of the rotor.

The housing 2 consists essentially of a single casting and contains the feedhopper 19,

the pulverizing and confining chamber 20 v'and the upper half of the cylindrical rotor "chamber 21, all of which c'o-operate with the rotor to pulverize the material in the manner to bef hereinafter described. The portion of the rotor chamber which is within the housing consists ofend walls 22, and the rear side lwalls 23, formed of the housing'casting, and

a. front wall 24 formed of a suitable curved plate which is adapted to be conveniently removed lto permit the inspection of the i-nterior arts of the machine.' All of the interior sur aces of thecasing which are exposed to the direct action of iiylng fragmentsof ma-y terial during thev pulverizing operation are protected with renewableplates of refractory metal as shown at 25, 26 and 27. Supported in suitable apertures of the casing are baiile bars 28, 29, 30 and 34 which extend longitudinally of the machine inclose proximity to the path of travel of the reducing elements or pulverizing surface-.to intercept the travel of material withthepulverizing surface as will be more fully hereinafter explained. Under some circumstances, to insure against the presence of oversize material in the product, suitably spaced longitudinally extending grate bars'32 may be arranged'beneath the rotor and supported in close proximity to the path of travel of theends of the arms 18 v by the fianges 33 formed on `the end walls of of material which may be carried around by' the casing, to retain unpulverized fragments within the iniiuence of the rapidly revolving arms 18 until such fragments are fully pul-4 verized. As ,illustrated in the drawings the baffle bar v28 extends inwardly to a point in close proximity to the pulverizing surface its urpose being to prevent the tangential pro- ]ection through the feed hopper of fragments the rotor. This baille bar 28 also forms the rearward limitation of the pulverizing chamber and ispositioned approximatelyiifty degrees behind the longitudinal vertical central plane of the rotor, its sides Abeing apj proximately parallel to. theradius 38 ofthe rotor which passes through the center ofsaid bar. Extending upwardly from the forward 4side of the bar 28 is" an inclined chute 39 formed of a web of the housing casting, and

" s upon this. chute material slides into the pulverizing chamber. At its upper end the chute 39 is turned forwardly in a volute 40-by which fragmentsof materialthrown from the pulby the line 29a in Fi 4. The forward wall of the pulverizing c amber is formed by a web 41 ofl the housing casting, extends upwardly as a continuationof the line 29a and islcurved rearwardly to form a helical scroll 42 the end of which is turned directly downward. Formed on the upper part of the scroll l 42 is an inclined ange, 43 to which 'is attached a plate 44 which co-'operates with the chute 39 yto form the feed hopper 19, and ywhich is adapted for adjustment in-the direction of its length to vary the vertical distance of the throat of the feed hopper from the pulverizing surface to regulate t-he flow of material into the pulverizing chamber. As shown in Fig. 2 material from the feed hopper 19 slides down the chute 39 'into the pulverizing chamber and floats upon the so called pulverizing surface to be pulverized'thereby. Under normal .operating conditions the rotor of the machine here illustrated revolves lat approximately two thousand revolutions per minute, causing the armsto assume a substantially .radial position, their ends describing a circular orbit which is indicated by the broken line 45 in Fig. 4. At such speed the arms pass 'a ygiven point in the orbit at the rate of twelve thousand per minute, or two hundred per second. Under these conditions, and making no allowance for the width of the arms 18, an unsupported block of material 46 immediately above and adjacent to the orbit 45, when acted upon by gravity `only, will fa-ll approximate# ly five thousandths of an inch after the pasder but rather as composed of saw tooth :shaped corrugations having aradial depth of five thousandths of an inch and a circular pitch of one sixth the circumference of the pulverizing cylinder, as indicated by the 'broken line 47 in Fig. 4. As the cylinder revolves these corrugations engage the block 46, chipping off minute particles of the material and tending to carry the entire block forwardly. As the engagement of the block 46 is below its center of gravity and its forward movement is resisted by its inertia, there is produced a rapid rotation of such block about its center of gravity, causing the corrugations of the pulverizing cylinder to contact with new points of'engagement on the block 46, chipping oli minute fragments at each contact, and reducing the block to a spherical form of ever decreasing dimensions. As the whirling block 46 is carried forward by the rotor it is intercepted by the baffle bar 29 as l indicated Fig. 4, producing a reaction similarJ'to-the carom-'o'f a billiard ball, which causes the said ,blockto ily. away from the l' rotor surface, following around the Ascroll 42,

lag. The amount of lag varies directly with the character of the material and the weight of the fragments. This rearward inclination of the arms 18, in conjunction with the forward inclination of the surface 41 at the lower end of the scroll 42, increases the upward reaction upon the block of material, thereby insuring the travel of the larger and heavier fragments around the scroll 42. Should the depth f material upon thepulverizing surface be sufficient to prevent the independent rotation of the-blocks of material upon theV pulverizing surface, and to also prevent their being thrown awayfrom'fthe roto surface against the scroll 42, the entire mass of matei' rial will lie quiescent upon the" pulverizing surface, in the manner of a brake-shoe, exerting a. .much eater retarding effect than is produced whlle the fragments are free to roll upon the pulverizing surface. When the fragments of material are thus held against freedom of movement the ends of the arms 18 will exert a cutting action similar to that of a planer tool, as illustrated in Fig. 5, materially increasing the power consumption and decreasing the amount' of the product. There is I itwill be found necessary, in order to attain also a tendency, when too great a volume of material is fed into the pulverlzing chamber, for such material to form an arch above the pulverizing surface, and entirely prevent further pulverizing action.

Experience has demonstrated that the most eiicient operation is obtained when the'line 51, drawn from the lower'edge-of the ad'ustable feed plate 44 to the surface of the p verizing cylinder at the vertical central plane of the machine, coincides with the vangle of repose of the material being pulverized. As the angle of repose is different for different characters of material maximum eiiciency, to change the adjustment v 'of the feed plate 44 to suit the characteristlcs y(ill of each different material which is to be pulverized. With suitable adjustment of the feeder late 44thel amount of material in the pulverizing cb amber will be so regulated that violent agitation of the fragments may be maintained, while the'maximum number of fragments will be in contact with the pulverizingcylinder,thereby producing a maximum quantity of product with a minimum of power consumptmn.

It will be seen; that by combining the closed y retaining or combining chamber with the reend and top walls of the confining chamber to the reducin elements. This maintainin uf the materia under constant and repeate action by the reducing-elements and preventing the escape of reduced material into the screening casing below the rotor, results in a uniformity of product and complete reduction -of the material.

It is apparent that the depth of the corrugations of the pulverizing cylinder will vary directly with the speed of revolution of the rotor,-ha ving greater depth with lower speed of revolution, and it has been found that the iinene'ss of the product bears a very close relation tothe speed of the rotor, it being finer as the speed is increased.

The baille bars 28, 29, 30', and 34are of polygonal cross section,.itwill lbe be noted, and are supported in apertures in the side walls of the casing, the apertures being of similar cross, section to ,that of the bars, in order to 'prevent theirfrotation. When the bars are in positiomthe apertures are closed by means of removable late 31. Referring to bar 29, for instance, 1t will be seen that it presents a deflecting edge (its lower right hand edge) in close proximity to the periphery of the rotor; When this edge becomes unduly worn in use,`plate 31 may be removed, bar 29-withdrawn from its supporting seats, and reinserted, Awith the new edgg in deflecting position.

Y the apparatus above described I have produced an improved pulverizing machine ofsimple and durableconstruction, economical of operation, and capable of pulverizing material varyingA in character from-such material as oats and similar light grains, to limestones of quarry size. e

2. In a pulverizin A machine, the combina- A tion with a rotor a apted to .revolve about a horizontal axis and having a substantially continuous cylindricalA pulverizing surface, of a pulverizing vchamber entirely above the e otor, means at the rearward side of the pulverizing chamber to feed material upon the pulverizing surface and permit it to freely oat thereon, means at theforward side of said chamber to prevent the escape of unpulverized material from said pulverizing chamber, and means to limit and control the the pulverizing surface and permit it to freely oat thereon, and means at the for. ward side of said pulverizing chamber to prevent the escape of unpulverized material from said pulverizing-chamber.

4. In a ,pulverizing machine, the combination with a rotor `adapted Ato revolve about a horizontal axis and having a substantiallycontinuous cylindrical pulverizing surface, of a pulverizing chamber entirely above said pulverizing surface, means to feed material withinthe pulverizing chamber upon the pulverizing surface and to permit it'to freely ioat thereon and means at the forwardv side of the pulverizing chamber' to prevent the escape of unpulverized material from the pulverizing chamber and to return unpulverized fragments of material towards the rearward part of said pulverizing chamber to be again acted upon by the pulverizing surface.

5. In a pulverizm machine, the combination with a -rotor a apted to revolve about a horizontal axis and having 'a substantially continuous cylindrical pulverizin surface, a pulverizing `chamber above sai rotor, an inclined chute at the rearward side of the pulverizing chamber upon' which material may slide to the pulverizing surface the outer end of said chute terminating in a forwardly disposed scroll`^adapted to intercept fragments of material thrown from the pulverizing chamber and return them thereto.

6. In a pulverizing machine, the combination with a rotor adapted to revolve'about a horizontal axisy and having a substantially continuous cylindrical pulverizing surface, a pulverizing chamber above said rotor, an inclined chute at the rearward side of said pulverizing'chamber upon which material may slide to the pul; verizing surface, and a gate for controlling the discharge from said chute.

7 In a pulverizing machine, the combination of a rotor adapted to-revolve about a horizontal axis and having a substantially continuous cylindrical pulverizing surface, al

pulverizing chamber above'said rotor, a baille at the forward side of theQpulverizing chamber in' close proximity to and above the horizontal axis of said rotor 'to intercept advanc- -continuous cylindrical pulverizin ing unpulverized fragments of material, and means to direct the' material intercepted by Isaid baille rearwardly to the pulverizingl surverized material to the upper side of sai rotor and prevent its passing downwardly into the throat of the machine while permitting it to float freel on said rotor. v

9. In a pu verizing machine, the combination with a rotor adapted to revolve about a horizontal axis and having a substantiallyy continuous cylindrical ulverizing surface, a pulverizing chamber a ove said'rotor positioned and arranged to confine the unpulverized material in' the upper side of said pulverizin cylinder while permitting it to freely oat thereon, an inclined chute at the rearward side of said pulverizing -chamber upon which material mayslide to the pulveri'zing surface, an oppositely inclined plate co-operating with said chute to form a feed hopper above said pulverizing surface said plate being adjustable to varyvlts vertical distance from .the pulverizing surface.

10. In a pulverizing machine, the combinat'on of a rotor ada ted to revolve about a horizontal axis andl aving a substantially v surface, of a pulverizing chamber above sai rotor, an inclined wall at the rear side of said u lverizing chamber to deliver material to e'pulfverized to thepulverizing surface and' permit 1t to oat freely thereon, and a curved wall to receive and direct the material pro-4 jected forwardl by the rotor upwardly and rearwardly to t e pulverizing surface.

111. In a pulverizing machine, the combina` tion of a rotor adapted to revolv'ecabout. a

horizontal axis and having asubstantially continuous cylindrical pulverizing surface,4 of a pulverizing chamber above said rotor,r an inclined wall at the rear side of said pul-l verizing chamber to deliver material to be pulverized to the pulverizing surface and permit it to Heat freely thereon, and a-wall aving a curved vertically disposed section.

and a. curvedrearwardly extending to sec-l tion to receive and direct they materia projected forwardly by the rotor upwardlyand rearwardly to the pulverizing surface.

12. In a pulverizing machine, the combination of a rotor adapted to revolve about a horizontal axis and having a substantially continuous cylindricalpulveriziug surface, a pulverizing chamber above said rotor, means at the rear side of said chamber to direct material to be pulverized to said rotor and perf mit it to oat freely thereon, a wall'at the forward side of said chamber having a continuous upwardly and rearwardly curved surface to intercept unpulverized material and return it to therear side of said chamber, and a baiile between the path of the rotor and said intercepting and returning means tor prevent the passage of unpulverized material downwardly with therotor.

13. In a pulverizing machine, the combination of 'a rotor adapt-ed to revolve about a horizontal axis and, having a substantially continuous cylindrical pulverizing surface, a pulverizing chamberv above said rotor, means at the rearward side of said chamber to rdeandsaid directing and returnin liver material to be pulverized to the pulverizlng surface and permit it to float freely thereon, lmeans at the forward side of said pulverizing chamber to receive and direct the material proj ected'forwardly by the rotor upwardly. and rearwardly and return it to the rear s1de of said chamber, andabaflie located between the path of movement of said rotor means to prevent the unpulverized materlal' passing downwardly with the rotor.

described, the

vfor reduced material, an enclosing opper for the material tof be/reduced arranged above and closely embracing, at its lower end, said rotor to retain the material in iioating4 condition on said rotor; and a material engaging abutment at substantially the junction of said casingiand hopper disposed in close relation to the path of rotation of vsaid reducin elements to permit the passage of comp etely reduced material only, said abutment having its material engaging face inclined to the vertical to 'deiect unreduced material upwardly and away from the rotor.

15. Ina machine of the class described, the combination of a rotor, a 4plurality of reducing elements disposed circumferentially of said rotor and which, when the rotor is in motion, generate a substantially continuous revolving material supporting surface; a casing closely surrounding the lower and major part of said rotor and having an outlet for reduced material; an enclosing hopper for the material to be reduced arranged above and closely embracing, at its .lower end, said rotor to retain the material 1n floating con? dition on said rotor; and a material engaging abutment arranged substantlally at the point of junction of said hop er and casing and extending in substantial y radial lines close to the path of rotation of said reducing elements.

16. In a machine of the class described, the

.of sai Acombination of arotor, -a plurality., of

ducing elements disposed clrcumferentially I of said rotor and which'when the rotor is ink motion, generate a substantially continuous y i revolvin material supporting surface; a casing close' y surrounding the lower and major part of said rotor and having an outletfor reduced material an enclosing hop er for the material to` be reduced arrang' above and closely embracing, at its lower end,said

' within the zone `of' action of said reducing elements; andmeans in said hopperto direct unreduced material upwardly-and rearwardlyand return it 'for repeated action by. said reducing instrumentalities.

y18. In a machine of the class described, the 'combination of a rotor, a plurality of'reducinge elements disposed `circu'xrrferential ly pf' -sai'dLrotor and which, when the rotor is 1n motion, generate a substantially continuous revolving material engaging surface a hopper to confine the materialto be reduced the zone of action of said reducing elements, said hopper havingjits inner wall shaped to direct the unreduced material upwardly and rearwardly and return itfor repeated action by said reducing 'instrumentalities.

19. In a machine'of the class'described' the combination of a rotor, la 4plurality o reducing elements disposed cnjcumferentiallyof said rotor, and which, when the rotor is in motion, generate a substantially continuous revolving material engaging surface; a hopper to confine the material to be reduced wit f in thezone of action of saidjreducing ele-A ments, said hopper having an upwardly'and rearwardly curved inner wall to direct the unreduced material upwardly and rearwardly and return it for repeated action by said reducing' 'instrumentalities f l 20. In a machine of the class les4 ;=ribed-,'tl`1e combination 'of reducing finstrumentalities', and a hopper provided with a material feedrotor to retain the material 1n floating condlroo ing chamber and a material 'confining Olamber communicating with said feeding chamber, said confining chamber being provided ber communicating with said feeding cham- Y ber, said conning chamber having an upu shape is wardl turn t e unreduced material to the reducing instrumentalities. y 22. In a machine of the class described, the combi-nationy of reducin instrumentalities, anda'hopper provided with a material feeding chamber and a material confining chamb 'er communicating `with said feeding chamber, said` confining chamber having a scroll d inner wall to return the unreduced material to the reducing instrumentalities.

23.' In a machine of the class described, the

- ifE.jr'annbination of reducing instrumentalities, a hopper provided \with a material feeding l, f2@ chamber and a material confining ,chamber ign communicating with said feeding chamber, a topA wall projecting partially across the top of said feeding chamber to prevent escape of material from said chamber, means in said .confining chamber to return unreduced material in an upward and rearward direction to the reducing instrumentalities, and adjustable means between said chambers to regulate the feed of material from said feeding chamber to said confining chamber.

24. In a machine of the class described, the combination of reducing instrumentalities, a hopper provided with a material feeding chamber and a material confining chamber.

'communicating with said feeding chamber, a

curved top wall projecting partially across the top of said feedlng chamber to prevent escape of material from said chamber, meansv in saidl confining chamber to return unreduced material in an upward and rearward direction to the reducing instrumentalities,

^ and adjustable means between said chamber to regulate the feed of material from said feedin chamber tol said confining chamber.

I a machine of the class described, the combination of reducing instrumentalites, a casing closely embracing a portion of said reducing instrumentalities, a hopper embracing' the unencased portion of said reducing instrumentalities, and an ,abutment on eac side of theunencased portion of said reducin instrumentalities extending in substanti y radial lines close to the path of rotation of said reducing elements to prevent unreduced material passing from eitherfside of .said'hopper into .the casing;

26. In -a machine of t e class described, the combination of reducing instrumentalities, a casing'closely embracing a portion of said reducing ins'trumentalities, a hop r embracing the unencased portion of sai reducing instrumentalities, an abutment at substantially the points of junction of said-hopper and casing on each side of the unencased portion of said reducing instrumentalities, and an abutment on each side of said reducand rearwardly curved wall to re- .material, a ragligly travelling attritive body,

ing instrumentalities below said first named abutments to prevent unreduced material passing-from either side of said, hopper into the casing.

27. In a machine for reducing friable lump means for'ccn ng a mass of feed material in operative contact with said bod and permitting the escapefrom such con ed area of only the completely reduced material, and means for. returning upwardly and rearwardl within said larea the unreduced material bisdplaced in the travelling direction of said 2g. The new and improved method of reducing friable lump material which consists in developing a rapidly rotating field of reducing action, feeding a mass of thematerial into a certain section of said field of action, sustaining the mass by the centrifugal effect produced in said field of action, confining said mass to substantially said 'feeling section, and permitting the escape from said section of only the completely reducedmaterial.

29. rihe new and improved method of reducing friable lump material which consists in developing a rapidly rotating field of reducingaction, feeding a mass of 'material into a certain section of said field of action, sustaining the mass by the centrifugal effect produced in said field of action, confining said mass to substantially said feeding section, returning upwardly and rearwardly within said section the unreduced material displaced in the travelling direction of said field, and permitting the escape from said section of only the completely reduced material. l

30. In a machine of the class described, a rotor comprising a plurality of reducing elements disposed circumferentially thereof, said elements generating a substantially continuous attritive surface when the rotor is in motion, means to confine a mass of material to be reduced in operative contact with said attritive surface, said means including an abutment element extendin longitudinally of the rotor at the rearwardimit of the confined mass in close proximity to said attritive surface, said abutment element having a substantially radial material obstructing and. deecting face to dei'ect unreduced material away from the rotor -while permitting passage beyond .said abutment element of completely reduced'material.

31. In al device of the class described, a

rotor, means for feeding material to be treatedf'to .the rotor, and -means to confine the means whereby the bar may be disposed therein in a selected edge in deflecting position.

32. In a machine of the class described,the combination of a rotor; a plurality of circumferentially disposed reducing elements arranged spirally-longitudinally of said rotor and which, when the rotor is in motion, generate a substantially continuous, revolving, material-supporting surface; anda hopper for the material to be reduced arranged above and. closely embracing at its lower end said rotor to prevent oversize material passing between said rotor and the lower end of said hopper. 4

33. In a machine of the class described, the combination of a rotor; a plurality of radially extending reducing elements circumferentially disposed and spirally arranged longitudinally of said rotor 'and which, when the rotor is in motion, generate a substantially continuous, revolving material-supportin surface; and a hopper for the material toe reduced arranged above and closely embracing at its lower end said rotor to prevent oversize material passing betweensaid rotor and the lower end of said'hopper.

34. In a machine of the class described, the combination of a movable member; a pluralhopper for the material to be reduced; a substantially vertical plate at the forward side of the hopper; and a laterall and lnwardly projecting abutment` at su stantially the lower end of said plate;

37. In a machine of the class described, the combination of a rotor; a plurality of reducing elements disposed circumferentlally of said rotorwhich, when the rotor is in motion, generate a substantially continuous revolving material engaging surface; a hopper for the material to be reduced; a, substantially vertical plate at the forward side of the hopper; and a laterally and inwardly projecting abutment having a downwardl inclined upper surface atsubstantially the lower end .of said plate.

In testimony whereof, I aiiix my signature.

WILLIAM KELSEY LIGGETT.

yso

ity-of reducing members carried by said member, and which, when the member is in motion, generate a substantially continuous, moving, material-engaging surface; .a hopper for the material to be reduced closely embracing at its rear lower end portion said movable member and reducing elements to retain the material in oating condition on Said reducing members and to prevent oversize material passing between said reducing elements and that end portion of said-hopper; and an adjustably mounted materialengaging abutment projecting close to the path of movement of said reducing elements.

35. In a machine of the class described the combination of a rotor, a plurality of reducing elements disposed circumferentially of said rotor, and which, when the ro-I tor is in motion generate a substantially continuous, revolving, material-engaging surface; a hopper for the material to be reduced closely embracing at its lower rear end a ortion of said rotor to retain the material 1n floating condition on said rotor and to prevent oversize material passing between the rotor and that end portion of said hopper; and an adjustably mounted materialengaging abutment projecting in substantially radial lines close to the path of rotation of said rotor.

36. In a machine of the class described, the combination of a rotor; a plurality of reducing elements dis osed circumferen- 

